module global

    ! Parameters that will be set by the user on the namelist.
    character(len=128) :: filename = "output.nc"
    integer :: idm, jdm, kdm, ldm, dldm
    real :: transport = 1e5
    real :: direction = 1.0
    real :: maxsteps = 1e4
    real :: interval = 86400.0
    logical :: cyclic_boundaries = .FALSE.

    ! Parameters that are calculated from the data and used by the algorithm.
    real, allocatable, dimension(:,:,:,:) :: ax, bx, gx, dx, ay, by, gy, dy, az, bz, gz, dz, dv
    real, allocatable, dimension(:,:,:,:) :: volume

    ! Constants.
    real, parameter :: R = 6371e3
    real, parameter :: PI = 3.1415

end module global
